A radio network includes two parts: radio access network and core network. A Long Term Evolution (LTE) radio core network includes a Mobility Management Entity (MME), which implements mobility management and user authentication like a Serving GPRS Support Node (SGSN) in a 2G/3G network. When the UE is idle in the 2G/3G network or the LTE network, the UE needs to negotiate Non-Access Signaling (NAS) security capabilities with the SGSN or MME to ensure normal receiving of the signaling and the security of the communication system.
When the UE in an idle state that accesses the network through an LTE radio access network, the UE may move to a routing area of a 2G GSM Edge Radio Access Network (GERAN) or a 3G UMTS Terrestrial Radio Access Network (UTRAN), and may access the access network through the 2G/3G network again. In this case, Routing Area Update (RAU) between Radio Access Technologies (inter-RAT) occurs; that is, an RAU process between heterogeneous networks occurs. In this process, the entity for negotiating security capabilities for the UE changes, for example, from an MME to an SGSN. The security capabilities of such entities are not necessarily the same. Therefore, it is necessary to perform the security capability negotiation process again to ensure security in the interaction between the UE and the network in the subsequent process.
When the UE moves from an LTE network to a UTRAN network, the RAU process involves negotiation of the ciphering algorithm and the integrity protection algorithm between the UE and the Radio Network Controller (RNC), and negotiation of the ciphering key and the integrity protection key.
When the UE moves from an LTE network to a GERAN network, the RAU process involves negotiation of the ciphering algorithm and the ciphering key between the UE and the 2G SGSN.
The prior art provides no method for negotiating security capabilities in the RAU process between heterogeneous networks. Therefore, when the UE moves from an LTE network to a 2G/3G network, the security capability negotiation is not supported, and the security is not ensured in the subsequent interaction between the UE and the network.